1. Field of the Invention
The present invention relates to an all primary combustion burner including a rectangular combustion plate in which a plurality of burner ports are formed and a burner main body of a box shape having an opening in which the combustion plate is inserted.
2. Description of the Related Art
Conventionally, among burners of this type, there is known a burner in which, with a longitudinal direction, a latitudinal direction, and a normal direction of a combustion plate set as an X axis direction, a Y axis direction, and a Z axis direction, respectively, a partition plate that demarcates a mixing chamber between the partition plate and a bottom wall section of a burner main body opposed to the combustion plate in the Z axis direction and a distributing plate that sections a space between the partition plate and the combustion plate into two chambers in the Z axis direction, i.e., a first distributing chamber on the partition plate side and a second distributing chamber on the combustion plate side, are provided in the burner main body. The burner mixes a fuel gas flowing into the mixing chamber from an upstream side in the X axis direction and a primary air in the mixing chamber to generate an air fuel mixture, guides the air fuel mixture from an outlet formed in the partition plate to the combustion plate through the first distributing chamber, a plurality of distributing holes formed in the distributing plate, and the second distributing chamber, and jets the air fuel mixture from burner ports of the combustion plate to subject the air fuel mixture to all primary combustion (see, for example, Japanese Patent Application Laid-Open No. 2001-90913).
In this burner, the outlet is formed in a slit shape long in the X axis direction and narrow in the Y axis direction. Consequently, an outflow of the air fuel mixture from the mixing chamber to the first distributing chamber is limited and the mixing of the fuel gas and the primary air in the mixing chamber is facilitated. However, a pressure loss in the outlet increases. Since the outlet is formed in the slit shape narrow in the Y axis direction, the air fuel mixture less easily flows to the portion of the first distributing chamber parting from the outlet in the Y axis direction. Therefore, to uniformalize the distribution of the air fuel mixture in the Y axis direction in the second distributing chamber, it is necessary to set an arrangement density of the distributing holes to be relatively low in the portion of the distributing plate located above the outlet. As a result, a pressure loss in the distributing plate also increases. To cope with the increase in the pressure loss in the outlet and the distributing plate, it is necessary to set a supply pressure of the primary air by a fan to be relatively high. As a result, noise increases.